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>41.4. Global Values in PL/Perl</A
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>    You can use the global hash <TT
CLASS="VARNAME"
>%_SHARED</TT
> to store
    data, including code references, between function calls for the
    lifetime of the current session.
  </P
><P
>    Here is a simple example for shared data:
</P><PRE
CLASS="PROGRAMLISTING"
>CREATE OR REPLACE FUNCTION set_var(name text, val text) RETURNS text AS $$
    if ($_SHARED{$_[0]} = $_[1]) {
        return 'ok';
    } else {
        return "cannot set shared variable $_[0] to $_[1]";
    }
$$ LANGUAGE plperl;

CREATE OR REPLACE FUNCTION get_var(name text) RETURNS text AS $$
    return $_SHARED{$_[0]};
$$ LANGUAGE plperl;

SELECT set_var('sample', 'Hello, PL/Perl!  How''s tricks?');
SELECT get_var('sample');</PRE
><P>
  </P
><P
>   Here is a slightly more complicated example using a code reference:

</P><PRE
CLASS="PROGRAMLISTING"
>CREATE OR REPLACE FUNCTION myfuncs() RETURNS void AS $$
    $_SHARED{myquote} = sub {
        my $arg = shift;
        $arg =~ s/(['\\])/\\$1/g;
        return "'$arg'";
    };
$$ LANGUAGE plperl;

SELECT myfuncs(); /* initializes the function */

/* Set up a function that uses the quote function */

CREATE OR REPLACE FUNCTION use_quote(TEXT) RETURNS text AS $$
    my $text_to_quote = shift;
    my $qfunc = $_SHARED{myquote};
    return &amp;$qfunc($text_to_quote);
$$ LANGUAGE plperl;</PRE
><P>

   (You could have replaced the above with the one-liner
   <TT
CLASS="LITERAL"
>return $_SHARED{myquote}-&gt;($_[0]);</TT
>
   at the expense of readability.)
  </P
><P
>   For security reasons, PL/Perl executes functions called by any one SQL role
   in a separate Perl interpreter for that role.  This prevents accidental or
   malicious interference by one user with the behavior of another user's
   PL/Perl functions.  Each such interpreter has its own value of the
   <TT
CLASS="VARNAME"
>%_SHARED</TT
> variable and other global state.  Thus, two
   PL/Perl functions will share the same value of <TT
CLASS="VARNAME"
>%_SHARED</TT
>
   if and only if they are executed by the same SQL role.  In an application
   wherein a single session executes code under multiple SQL roles (via
   <TT
CLASS="LITERAL"
>SECURITY DEFINER</TT
> functions, use of <TT
CLASS="COMMAND"
>SET ROLE</TT
>, etc)
   you may need to take explicit steps to ensure that PL/Perl functions can
   share data via <TT
CLASS="VARNAME"
>%_SHARED</TT
>.  To do that, make sure that
   functions that should communicate are owned by the same user, and mark
   them <TT
CLASS="LITERAL"
>SECURITY DEFINER</TT
>.  You must of course take care that
   such functions can't be used to do anything unintended.
  </P
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